A one-belt type seat belt device having to tongue and buckle is known, for example, from U.S. Pat. No. 3,844,001. Its summary is as shown and explained hereinbelow with reference to FIG. 13.
Because the conventional seat belt is made of thin cloth, it is not only difficult to operate, but also the front surface and back surface of the belt are difficult to discern from each other. Therefore, the belt is likely to be twisted by mistake, and the fitted belt is likely to rise in the twisted portion and hurt the neck or other part of the rider.
Further, the operation of fitting this kind of conventional seat belt device to a tongueless buckle in locking requires two steps, viz., the operation of inserting the seat belt, and the operation of locking the inserted belt. These operations are difficult and complicated.
Also, when inserting the seat belt in the tongueless buckle, because the belt is thin and is made of cloth, it will flex when it is inserted. Thus, a one-touch type tongueless buckle which can be automatically locked and fitted by only the inserting operation can not be achieved with the conventional components and structure.